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copied!<p>Instead of having two lists just use a <code>Map<String, List<Station>></code>. The <code>trainNumber</code> would be the unique key and you could easily add or delete stations from the corresponding list in the map.</p> <p><strong>UPDATE</strong></p> <p>As suggested by @ipavlic use <code>Map<String, Set<Station>></code>, since a set allows no duplicate elements.</p> <p><strong>UPDATE2</strong></p> <p>Here a little example, with some comments. The example shows you just how to use a map combined with a set. You should <strong>not</strong> copy this into you code 1:1, since this is not a object-oriented approach. The map should be encapsulated in some object.</p> <pre><code>import java.util.HashMap; import java.util.Map; import java.util.Set; import java.util.TreeSet; public class MapSetExample { public static void main(String[] args) { Map<String, Set<String>> map = new HashMap<String, Set<String>>(); System.out.println("ADDED = " + add(map, "Train1", "Station1")); System.out.println("ADDED = " + add(map, "Train1", "Station2")); System.out.println("ADDED = " + add(map, "Train1", "Station1")); System.out.println("Stations of Train1 = " + map.get("Train1")); } private static boolean add(Map<String, Set<String>> map, String key, String station) { Set<String> set = map.get(key); /* If map.get() returns null, that means there is no set * in the map associated with given key. * * In that case we create a new set. * * If there is already a set, we use that one. */ if (set == null) { set = new TreeSet<String>(); map.put(key, set); } /* False if station is already in set. At this point you could also delete sth. etc. */ boolean success = set.add(station); return success; } } </code></pre> <p><strong>OUTPUT</strong></p> <pre><code>ADDED = true ADDED = true ADDED = false Stations of Train1 = [Station1, Station2] </code></pre>

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